I bought a new AK, and it wouldn't lock any mags in - not even the Magpul PMAG that came with it.  You could whack the mag forward and watch it fall out.  The mag catch caught on the end of the magazine's locking tab and didn't even start up the "ramp" at all.  So I filed down the top of the mag catch, and it locks in great now.  Has a nice click when the mag catch slides up the ramp and pops against the mag body, and it holds the mags in tightly now.  It works with all my plastic mags, and my surplus Russian and mixed European mags lock in great now too.

It shoots great with the plastic mags (Promag and Magpul).  But when I insert a metal mag and try to charge the rifle, the bottom of the bolt scrapes back along the top round in the mag and hangs on the lip of the steel case on my Golden Tiger ammo.  It seizes up and won't pull any farther back once it hits that casing lip.  And it scratches the crap out of the top round.  It does that with 4 out of the 12 surplus steel mags I tried.  Any ideas?  Should I file some more off the mag catch so the mags have some up/down wobble instead of being so tight?  My other AKs have all kinds of wobble in all directions (WASRs, mostly).  They love steel mags.  I'm afraid if I file too much off I will have feeding issues.

Any feedback would be appreciated.

I emailed the manufacturer.  A guy there told me to file more off the mag catch and see if that fixed it.  It seems to have done the trick.  At least the AK charges now with the problem metal mags.  They have a little bit of up/down wiggle now - I thought they should be tight.  Guess not.

filing the mag catch is exactly the wrong answer.  Yes, sometimes a mag catch needs to be filed, but only after the selector stop plate has been machined  so that the mag bottoms out on the rails.  Then if is still is too tight, adjust the height of the mag catch.  Doing it out of order cause the mag to hang too low.

I think I understand what you're saying about the bolt dragging on the cartridge case, but It doesn't compute.  What receiver is it?  It sounds like the rails are too high.  And correct rail height is presupposed in adjusting mag fit.

The max allowable up and down movement of a 7.62 mag is 0.5mm.  Push up, scribe a line, pull down, scribe a l;ine.  Must be no more than 0.5mm.  

The magazine does bottom out on the rails when fully inserted.  The mag catch wouldn't "catch" the mag at all until I filed it.  I think I just didn't file enough.  The metal mags latched in really tightly with no wiggle at all.  I don't know what kind of lower receiver DDI uses on their stamped AKs, but I am hopeful now that it will work 100% when I get a chance to test fire it again (hopefully this weekend).

It worked great after my filing before as long as I didn't use those 4 metal mags.    I just hope I didn't screw the plastic mag function up.  Steve @ DDI told me that if I did screw it up, they'd take the rifle back and fix it.  I just thought I would post here first to see if I was pointed in the right direction, but after getting no quick responses, I emailed DDI and got directions and a "don't worry - we'll make it right" response.

My "firing range" is my in-laws' cow pasture like 15 minutes from here, but I can't ever get to it because of work and multiple projects tying me up.  Got my fingers crossed that this weekend will be the next range trip.  

Thanks for the info!

Edit to add:  Range trip went great - 100% function with all my mags now.  Problem solved by proper application of a thin file to the top of the mag catch.

'after the selector stop plate has been machined so that the mag bottoms out on the rails.'

What 'rails' are you referring to?

receiver rails.